Java 语法

Java 语法过关。

看注释理解，有其他语言基础还是容易上手的。
（ Java 手敲起来看着很长，但是用上 IDEA 就会有种被读心的感觉）

基本框架

dfs 求全排列。

// 导入包
import java.io.*;
import java.util.Scanner;

public class Main {
    
    // 定义全局变量
    private static int[] res;
    private static boolean vis[];
    private static int n;
    private final static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

    // 主函数
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        res = new int[n];
        vis = new boolean[n];
        dfs(0);
        bw.flush();
    }

    // 自定义函数
    private static void dfs(int u) throws Exception {
        if (u == n) {
            for(int i = 0; i < n; i++){
                bw.write(res[i] + " ");
            }
            bw.write("\n");
            return;
        }

        for(int i = 0; i < n; i++) {
            if(vis[i]) continue;

            res[u] = i + 1;
            vis[i] = true;
            dfs(u + 1);
            vis[i] = false;
        }

    }
}

类的使用

三元组的排序。

import java.util.Arrays;
import java.util.Scanner;

class tuple implements Comparable<tuple> {
    // 定义成员变量
    int x;
    double y;
    String z;

    // 构造函数
    public tuple(int x, double y, String z) {
        this.x = x;
        this.y = y;
        this.z = z;
    }

    // 实现接口 Comparable<tuple>
    public int compareTo(tuple o) {
        return x - o.x;
    }
    
    // 成员函数
    public void output() {
        System.out.printf("%d %.2f %s\n", x, y, z);
    }

}

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        tuple[] a = new tuple[n];
        for (int i = 0; i < n; i++) {
            a[i] = new tuple(sc.nextInt(), sc.nextDouble(), sc.next());
        }
        Arrays.sort(a);
        for (int i = 0; i < n; i++) {
            a[i].output();
        }
    }
}

继承、多态与接口

import java.util.Scanner;

// 定义接口
interface Role {
    public void greet();
    public void move();
    public int getSpeed();
}

// 继承接口
interface Hero extends Role {
    public void attack();
}

// 多个类实现接口
class Athena implements Hero {
    private final String name = "Athena";
    public void attack() {
        System.out.println(name + ": Attack!");
    }

    public void greet() {
        System.out.println(name + ": Hi!");
    }

    public void move() {
        System.out.println(name + ": Move!");
    }

    public int getSpeed() {
        return 10;
    }
}

class Zeus implements Hero {
    private final String name = "Zeus";
    public void attack() {
        System.out.println(name + ": Attack!");
    }

    public void greet() {
        System.out.println(name + ": Hi!");
    }

    public void move() {
        System.out.println(name + ": Move!");
    }

    public int getSpeed() {
        return 10;
    }
}

public class Main {
    public static void main(String[] args) {
        Hero[] heros = {new Zeus(), new Athena()};
        for (Hero hero: heros) {
            // 多态 共用hero接口
            hero.greet();
        }
    }
}